The present invention is directed toward a reinforcing structure useful for reinforcing a variety of elements. Specifically, the reinforcing structure is a cord defined by core filaments and a helical wound wrap wire. The structure is designed for both compressive and tensile loading conditions.
Metallic cord structures can be successfully used as the reinforcement means in composites wherein the materials to be reinforced are elastomers, reinforced plastics, and cementious systems. Traditional cord structures found in tire constructions are known to work well in these composites, especially when the application of the composite is dominated by a tension stress state. However, using traditional cord structures, there are limitations to the use of composite systems when the application in which the composite is applied is subjected to compression stress states.
There are four factors that contribute to low compressive behavior in composites made with typical metallic cord structures. They are 1) low composite packing density due to asymmetric cord structures or inefficient intra-cord packing due to geometrical interference, 2) kinks caused by permanent deformations of the core filaments (usually found in cords constructed in accordance with U.S. Pat. No. 4,022,009, such as a 3xc3x972), 3) core filament misalignment (typical of cords such as a 12xc3x971), and 4) small core filament diameter and lack of support.
U.S. Pat. No. 4,718,224 discloses a cord for reinforcing elastomeric structure, in particular, tire belt plies. The cord has a wrapped construction wherein the core has a plurality of aligned center filaments such that one axis of the cord has a greater dimension that the perpendicular axis. This cord exhibits greater tensile properties along the greater axis, but is insufficient when subjected to compression stress states due to the unequal axis.
The present invention is directed toward a reinforcing structure designed for handling compression stress states when molded into a composite. The structure, specifically a wrapped cord with metallic filaments contained therein, is suitable for both compression and tension load forces.
The reinforcing structure has a core comprising a plurality of essentially straight, nested filaments arranged in parallel, the filaments forming a line of contact with adjacent filaments that extends along the length of the filaments. Wrapped about the core is at least one helically wound wire.
In one aspect of the invention, all of the nested filaments in the core are formed from metallic filaments. The filaments may have a diameter of at least 0.30 mm.
In another aspect of the invention, the helically wound wires have a diameter less than the diameter of the nested filaments. The helically wound wires have a diameter in the range of 0.10 to 0.30 mm. The helically wound wires may be wound at a helix wrap angle less than the buckling wave length of the nested filaments. The buckling wave length of the nested filaments is approximately equal to the square of the core filament diameter. However, the helix wrap angle may be optimized for cost effective support of the core filaments in compression, resulting in a helix wrap angle of greater than the buckling wave length.
In another aspect of the invention, the nested filaments are essentially straight and have a twist lay length of greater than 30 mm. Preferably, the twist lay length is infinity, resulting in straight core filaments.
In another aspect of the invention, to increase the compression force capability of the cord, within any interstices formed in the core between the nested filaments and between the nested filaments and the helically wrapped wires, fiber filaments may be placed.
The fiber filaments placed in the interstices may be selected from the group of glass, carbon, cotton, KEVLAR, polypropylene, nylon, polyester, aramid, wool, and metallic fibers such as aluminum, titanium, beryllium or other like filament or fiber.
In another aspect of the disclosed invention, a composite is formed. The composite is formed from the disclosed reinforcing structure and a binding matrix. The binding matrix may be selected from the group the group of elastomer, thermoplastic, cement mixes, and wood laminates.
In yet another aspect of the invention, the reinforcing structure may be formed into a tape. The tape has multiple reinforcing structures aligned and fixed in parallel to one another. To secure the structure of the tape, the reinforcing cords may be woven, glued, or secured together by other means in any manner that will maintain the orientation of the cords relative to each other.
Definitions
The following definitions are applicable to the present invention:
xe2x80x9cCompositexe2x80x9d means a material containing both a reinforcement means and a binding matrix or resin. The binding matrix or resin may be types of elastomers, thermoplastics, wood laminates, or cement mixes. Within the context of this invention, the reinforcement means is a multi-filament cord or a fabric, tape, or sheet formed from a multi-filament cord.
xe2x80x9cCordxe2x80x9d means a plurality of gathered filaments to form a unitary structure.
xe2x80x9cNormal Tensile Strength (NT) Steelxe2x80x9d means a carbon steel with a tensile strength of at least 2800 MPa @ 0.20 mm filament diameter.
xe2x80x9cHigh Tensile Strength (HT) Steelxe2x80x9d means a carbon steel with a tensile strength of at least 3400 MPa @ 0.20 mm filament diameter.
xe2x80x9cSuper Tensile Strength (ST) Steelxe2x80x9d means a carbon steel with a tensile strength of at least 3650 MPa @ 0.20 mm filament diameter.
xe2x80x9cUltra Tensile Strength (UT) Steelxe2x80x9d means a carbon steel with a tensile strength of at least 4000 MPa @0.20 mm filament diameter.
xe2x80x9cMega Tensile Strength (MT) Steelxe2x80x9d means a carbon steel with a tensile strength of at least 4500 MPa @ 0.20 mm filament diameter.